Optical Wavelength Division Multiplexing (WDM) has the potential to significantly improve network capability and reliability via redundancy. Redundancy is particularly important in critical applications, such as on mobile platforms of various forms, and particularly in aircraft and aerospace applications. However, to be useful, WDM networks must be maintainable. Optical Link Loss (OLL) measuring and Optical Time Domain Reflectometry (OTDR) are powerful techniques for diagnosing the health of the passive elements of a photonic network, such as fiber optic cables. However, WDM networks present new troubleshooting and maintenance challenges because applying the above-described techniques can be a complex process. The reason for the complexity is that no one wavelength of a WDM network can be used to probe all paths through a network. This is because a given wavelength will rarely be present in every single path in a complex optical network. Thus, a source for providing a test signal for every wavelength present in the network must be provided. In aircraft and aerospace applications, the addition of multiple wavelength test signal sources into ground support equipment would make the equipment unacceptably expensive. The addition of multiple wavelength sources into on-board test systems is unacceptable due to the significant weight, volume and cost increases that such multiple wavelength sources would cause.
Accordingly, there still exists a need for an optical WDM network that enables every wavelength implemented in the network to be checked without the need for introducing significant additional test equipment. The ability to be able to test the network continuously, in real time, and without disrupting/affecting the transmission and reception of data over each path/channel of the network is also an important consideration.